ultimate postulate of all real science—the postulate of the uniformity of nature. He stood quite close to Spinoza in this respect without being aware of it.
Kant's mind was likewise occupied with various other problems during this period. His conclusion concerning the distinction between philosophy and mathematics is noteworthy, namely, that philosophy cannot create its concepts as mathematics does. It derives its concepts from experience. Hence, inasmuch as experience is never universal, philosophy is limited to imperfect concepts. The concept of soul, for example, is an imperfect concept; experience furnishes no warrant for speaking of a psychical substance. In the ingenious brochure, Traume eines Geistersehers, erlaütert durch Traüme der Metaphysik (1766), Kant shows, partly in satire, how easy it is to construct a system of the supersensible world. The only requirement is a naive implicit confidence in our concepts as complete and final.
The concept of causality is another example of an incomplete concept. How can the analysis of a given phenomenon reveal the necessity of another phenomenon? But the concept of causality assumes precisely this necessity! K ant therefore (even in the essay: Versuch den Begriff der negativen Grösse in die Weltweisheit einzuführen, 1762) approaches the problem of causality in precisely the same form in which it had been stated by Hume. Kant's later remark that it was David Hume that roused him from his dogmatic slumbers, with its evident reference to Hume's criticism of the concept of causality, would indicate that this awakening took place as early as 1762. (Students of Kant differ widely on this point however.) It is impossible to describe the years in which Kant was occupied with the study of the causal concept and
